This invention relates generally to a method of forming composite structures and, more particularly, to such a method that employs an intrusion molding process.
Composites are utilized in many applications requiring defined structures exhibiting both relatively high strength and low weight. Such composites generally consist of laminates joined together to provide an integral structure having the combined physical and chemical characteristics of the materials utilized. Frequently used materials include thermal setting resins and high strength fiberglass cloth. A well known composite to which the present invention is directed consists of resin impregnated fiberglass cloth laminated over a syntactic foam core composed of small hollow spheres embedded in a resin matrix.
One prior method of producing syntactic foam cored fiberglass laminates includes the steps of casting the syntactic core, laminating and curing resin impregnated fiberglass into opposing skin halves to form a shell, preparing and bonding the core between the skin halves, laminating resin impregnated fiberglass reinforcement around the seams between the core and the laminate and sanding and preparing the outside surface of the laminate to the required dimensions. This method is highly labor intensive because of the requirements for preshaping the core to fit between the laminate skins, matching the skin halves to facilitate a close fit at the seams and overlaying and finishing the seams. Other disadvantages are that the method fails to produce complete contact between the core and the skin laminate thereby creating areas of weakness and the completed composite exhibits a seam rather than a continuous outer skin.
Another prior method of producing syntactic foam cored fiberglass laminates includes the steps of casting the core, preparing the core for laminate, laminating resin impregnated fiberglass cloth around the core, vacuum bagging and curing the wrapped laminate and machining the outside surface of the laminate to the required finish. This method also is labor intensive because of the significant requirements for laminate machining to establish the required finish. In addition, sharp outside corners cannot be molded and the final outside shape of the composite is somewhat irregular.
The object of this invention, therefore, is to provide an improved method of producing composites consisting of a fiberglass reinforced plastic laminate enclosing a syntactic foam core.